1. Field of the Invention
The invention relates generally to display systems and, more specifically, to a method and apparatus for controlling sparse refresh of a self-refreshing display device coupled to a graphics controller.
2. Description of the Related Art
Computer systems typically include some sort of display device, such as a liquid crystal display (LCD) device, coupled to a graphics controller. During normal operation, the graphics controller generates video signals that are transmitted to the display device by scanning-out pixel data from a frame buffer based on timing information generated within the graphics controller. Some recently designed display devices have a self-refresh capability, where the display device includes a local controller configured to generate video signals from a static, cached frame of digital video independently from the graphics controller. When in such a self-refresh mode, the video signals are driven by the local controller, thereby allowing portions of the graphics controller to be turned off to reduce the overall power consumption of the computer system. Once in self-refresh mode, when the image to be displayed needs to be updated, control may be transitioned back to the graphics controller to allow new video signals to be generated based on a new set of pixel data.
When in a self-refresh mode, the graphics controller may be placed in a power-saving state such as a deep sleep state. In addition, the main communications channel between a central processing unit (CPU) and the graphics controller may be turned off to conserve energy. When the image needs to be updated, the computer system “wakes-up” the graphics controller and any associated communications channels. The graphics controller may then process the new image data and transmit the processed image data to the display device for display.
One drawback to updating the image is that “waking-up” the graphics controller and associated communications channels may take a significant amount of time. For example, waking up a PCIe bus may take 70-100 ms or more. Such delays introduce latencies between the time the CPU attempts to update an image and the time the processed image is displayed via the display device. When frequently entering and exiting a self-refresh mode, such delays may become distracting to a user of the computer system. Furthermore, the computer system may consume unnecessary amounts of energy in order to initialize the graphics controller and associated communications channels for relatively minor tasks.
As the foregoing illustrates, what is needed in the art is an improved technique for updating the cached frame of video data in a self-refreshing display device.